Field of the Invention
The invention relates to a control unit for a motor vehicle having an automatic transmission, including a transmission control unit and an engine control unit which are connected to one another by a communication channel through which data bringing about a reduction in engine torque when the transmission ratio of the transmission is modified, are transferred from the transmission control unit to the engine control unit.
Such control units in a motor vehicle with an automatic transmission include an engine control unit and a transmission control unit. They are available in different constructions.
In a known integrated control unit for the automatic transmission and the engine of a motor vehicle, the transmission is controlled by an independent control device which is separate from the engine control unit (as disclosed in U.S. Pat. No. 4,945,489).
In a step-by-step variable speed transmission, a transmission control unit essentially has to carry out the following functions:
a gear-shift control which ensures a gentle and abrasion-free engagement of the individual gears; PA1 a control of the converter lockup clutch; PA1 a gear-shift logic which determines the gear to be respectively engaged; PA1 self-testing; and PA1 basic functions such as, for example, input and output functions. PA1 regulation of a desired transmission ratio; PA1 control of a starting-up clutch and a converter lockup; PA1 calculation of the desired transmission ratio; PA1 execution of self-testing; and PA1 control of basic functions. PA1 the gear-shift control of a step-by-step variable speed transmission and the regulation of the desired transmission ratio in the case of an infinitely variable speed transmission are referred to uniformly as shift control; and PA1 the switching logic of a step-by-step variable speed transmission and the calculation of the desired transmission ratio in the case of an infinitely variable speed transmission are referred to uniformly as transmission ratio selection.
In the case of an infinitely variable speed transmission, a transmission control unit has to carry out the following functions:
In order to ensure that identical terms can be used below for a step-by-step variable speed transmission and for an infinitely variable speed transmission,
Since the shift control has to be configured in a transmission-specific way while the configuration of the transmission ratio selection depends, inter alia, on data from the engine and from the chassis of the motor vehicle, a large number of different variants of the control unit for the various types of motor vehicle results. Furthermore, the expenditure for the cable harness between the transmission control unit and the various valves and sensors in the transmission is extremely high.